Solid state regulated power supply for intermittent loads with plural charging paths for a capacitor

ABSTRACT

A VOLTAGE REGULATOR FOR USE WITH INTERMITTENT LOADS SUCH AS FLASH LAMPS WHICH REQUIRE HIGH VOLTAGE PULSES. THE REGULATOR SUPPLIES VOLTAGES WHICH VARY FROM A REGULATED MAXIMUM BETWEEN FLASHES TO SUBSTANTIALLY ZERO AT THE END OF A FLASH. SINCE THE VOLTAGE OF THE REGULATOR GOES SUBSTANTIALLY TO ZERO AT THE END OF THE FLASH, RAPID REPETITION OF THE FLASH IS MADE POSSIBLE.

SOLID STATE REGULATED POWER SUPPLY FOR INTElllIlTEI'I I F b, 2,1971 F. CAPRARI 3,560,842

LOADS WITH PLURAL CHARGING PATHS FOR A CAPACITOR Filed D66 26, 1968 Q I as Fou ng} Cdprari I TOR United States Patent US. Cl. 323-22 6 Claims ABSTRACT OF THE DISCLOSURE A voltage regulator for use with intermittent loads such as flash lamps which require high voltage pulses. The regulator supplies voltages which vary from a regulated maximum between flashes to substantially zero at the end of a flash. Since the voltage of the regulator goes substantially to zero at the end of the flash, rapid repetition of the flash is made possible.

This invention relates to power supply devices that are particularly adapted to supply an intermittent load, that is a load that requires a high voltage followed very quickly by substantially zero voltage, such, for example, as flash lamps.

When a high voltage trigger pulse is applied to a flash lamp, the gas therein ionizes and the impedance of the lamp becomes very low. Furthermore, the condition of ionization continues even though the voltage applied to the lamp goes lower than the ionizing voltage, whereby the lamp does not go off unless the voltage applied thereto goes down to a very low value. The lamp cannot be flashed again until it goes off. Also, the lamp while ionized continues to draw current, greatly loading the voltage supply. Therefore, for providing discrete flashes by a flash lamp, high voltage must be applied thereto to cause ionization of the gases in the flash lamp to provide the flash. The high voltage must almost immediately be reduced to a very low value to permit the flash lamp to become deionized to permit further flashing at short intervals. Furthermore, to assure that the intensity of successive flashes does not vary, the voltage of the power supply must build up rapidly to the same predetermined voltage between successive flashes. In a known regulating power supply which includes a voltage regulating element and a control element for the regulating element, the voltage across the regulating element drops very low between flashes whereby the regulating element loses control of regulation. Furthermore, due to the rapid change in the voltage across the flasher, the control element controlling the conductivity of the regulating element does not properly control the regulating element. Also, in the known regulator, the voltage applied to the load is limited by the voltage that may safely be applied across the control element. Furthermore, the power supply efiiciency is lower than desired.

According to the invention, a voltage regulator including two sources of voltage, is provided, said voltage regulator including a storage capacitor in which the energy required to cause a flasher to flash is stored. The energy that is stored is supplied to the storage capacitor over two paths. 'One of said sources is connected to apply a nearly constant voltage across the control element of the voltage regulator and to apply a keep alive voltage to the regulator element. The maximum current applied across the regulator element is reduced and also the efliciency of the power supply is increased since the regulator element regulates only the portion of the voltage that is applied to the capacitor through one of said paths.

The invention will be better understood by reading the 3,560,842 Patented Feb. 2, 1971 following description in connection with the single figure of the drawing which illustrates an embodiment of this invention.

Turning to the figure, a three winding iron core trans former 10, which may be of the constant voltage type if desired, is provided. The primary winding 12 of the transformer 10 may be connected across a source of alternating current not shown. The terminals of a first secondary winding 14 are connected to respective anodes of rectifying diodes 16 and 18. The cathodes of the diodes 16 and 18 are connected to respective anodes of rectifying diodes 20 and 22, and the cathodes of the diodes 20 and 22 are connected together and through a current limiting resistor 23 to the cathode of a Zener diode 24. If convenient, one diode may be substituted for each of the pairs of diodes 16 and 20 or 18 and 22. The center tap of the winding 14 is connected to the anode of the Zener diode 24 and to ground 28. A voltage sensing and storage capacitor and a storage capacitor 32 are connected in the order named between the cathode and the anode of the Zener diode 24. The load 34, which may be a flash lamp or a pulsed laser, is connected across the storage capacitor 32. The load 34 is provided with a triggering terminal 36.

One terminal of the second secondary winding 38 of the transformer 10 is connected to the cathode of a rectifying diode 40 and to the anode of another rectifying diode 42. The other terminal of the winding 38 is connected to a point between two capacitors 44 and 46 which are connected in series between the anode of the diode 40 and the cathode of the diode 42, whereby a doubled direct voltage, which is provided by the voltage doubler 47 comprising the elements 38, 40, 42, 44 and 46, appears across the two capacitors 44 and 46 in series in a known manner. The anode of the diode 40 is connected to the collector of a NPN transistor 48. The cathode of the diode 42 is connected through a resistor 54 to the base of a NPN transistor 56 and to the collector of an NPN transistor 58. The collector of the transistor 56 is connected to the collector of the transistor 48 and the emitter of the transistor 56 is connected to the base of the transistor 48. It will be noted that the voltage doubler 47 supplies a current to the collector of the transistor 58 which is nearly constant. Since it is known that variation in current supply to the collector of the transistor 58 causes error in the regulation provided by the transistor 58, this nearly constant current supply makes for better voltage regulation by the described regulator.

The emitter of the transistor 48 is connected through a current equalizing resistor 50 and a current limiting resistor 52 in series to the junction of the storage capacitor 32 and the load 34.

The emitter of the NPN transistor 58 is connected to the cathode of the Zener diode 24, and the base of the transistor 58 is connected to terminals of two resistors 60 and 62. A variable resistor 64 is connected between the junction of the resistors 50 and 52 and one terminal of the resistor 60. The other terminal of the resistor 62 is connected to the anode of the Zener diode 24. A connection 65 is made between the collector of the transistor 48 and the cathode of the diodes 20 and 22. A filter capacitor 66 is connected across the resistors 60 and 64, and a further filter capacitor 68, which may be several filter capacitors connected in parallel if desired, is connected between the anode of the diode 40 and the anode of the Zener diode 2-4.

A bleeder resistor 70 is connected between the base of the transistor 48 and its emitter. A pair of resistors 72 and 74 are connected in series between the junction of the two resistors 50 and 52 and the base of the transistor 48. The base of a NPN transistor 76 is connected to the base of the transistor 48 and the collectors of the transistors 48 and 76 are connected together, while the emitter of the transistor 76 is connected to the junction of the resistors 72 and 74. The resistors 50 and 72 act to equalize the current flow through the two parallel connected series regulating transistors 48 and 76. If desired, a voltmeter 78 is connected between the junction of the rsistors 50 and 52 and the anode of the Zener diode 24.

In explaining the operation of this device, it will be assumed that an A.C. voltage is applied across the primary winding 12 and that no triggering pulse is applied to the triggering terminal 36. Then, since the direct voltage supplied by the full wave rectifier 80 comprising the elements 14, 16, 18, and 22 across the Zener diode 24 is higher than the break down voltage thereof, the Zener diode .24 breaks down, the resistor 23 protecting the Zener diode 24 and the rectifier 80. Since the capacitors and 32 are about the same size, the capacitor 32 charges to about one half the break down voltage of the Zener diode 24. As previously stated, the voltage doubler 47 applies a nearly steady direct current to the collector of the transistor 58. The voltage doubler 47 in series with the full wave rectifier power supply 80 supplies collector current for the transistor 58 and base current for the transistors 48, 56 and 76. The transistors 48, 56 and 76 therefore become fully conductive during the operation of the described circuit. Charging current for the capacitor 32 flows from the cathode of the diodes 20 and 22, through the connection 65, the collector to emitter paths of the transistors '48 and 76, the current equalizing resistors 50 and 72, the current limiting resistor 52 and into one terminal of the storage capacitor 32, it being noted that the other terminal of the storage capacitor 32 is connected to the center tap of the winding 14. Therefore, initial charging of the capacitor 32 is provided by way of the resistor 23 and additional charging of the capacitor 32 is provided by way of the transistors 48 and 76 and the resistor 52. The voltage across the resistors 64, and 62 in series varies very rapidly, while the voltage across the capacitor 32 varies at a much slower rate, due to the operation of the resistor 52. The maximum voltage across the capacitor 32 is determined by the setting of the variable resistor 64.

The capacitor 32 reaches a regulated voltage in a very short time. The flash tube comprising the load 34 is flashed by applying a triggering voltage to the triggering terminal 36. The gas in the flash tube ionizes and the resistance thereacross goes to a fraction of an ohm. The capacitor 32 discharges through the load 34 very quickly. The resistance of the path to ground through the Zener diode 24 for the capacitor 30 is much higher than the resistance of the path to ground for the capacitor 32 (it being noted that one terminal of the capacitor 32 is grounded) whereby the capacitor 30 contributes little to the flow of current through the load 34, most of the charge of the capacitor 30 remaining. However, as much current flows into the load from the capacitor 30 as flows into the capacitor 30 through the resistor 23, whereby the voltage across the Zener drops to zero. Since the standard voltage is zero, the transistors 48 and 76 become fully non-conductive and the voltage across the meter becomes substantially zero. The flash tube deionizes whereby its resistance goes high again and the charge in the capacitor 30 spills into the capacitor 32. The voltage across the Zener diode 24 again goes to its breakdown voltage and the transistors 48 and 76 become conductive again and the voltage across the capacitor 32 again builds up the voltage determined by the setting of the resistance 64 and the cycle is completed. Upon applying a starting voltage to the starting terminal 36, the discharge and charge cycle of the described regulator is repeated.

Since in the circuit as described, the source comprising the doubler 47 supplies transistor current but does not supply a substantial amount of load current, the current variation across the control transistor 58 is substantially reduced over a known regulator in which one source supplies both currents, resulting in better control regulation. Also, due to the fact that the doubler 47 continually supplies biasing current for the transistors 48 and 76, the voltage across the emitter and collector of the pass and regulating transistors 38 and 76 may go down to a few volts without losing regulation. Also, the collector current of the transistors 76 and 48 is reduced and the power efficiency of the described regulator is increased over known regulators in which only one source of supply is provided. This is due to the fact that the capacitor 32 is charged by the capacitor 30, without going through the transistors 48 and 76; to about one-half of the breakdown voltage of the Zener diode 24. Reduced collector current for the transistors 48 and 76 also results in lower collector dissipation in these transistors and in more stable operation. It is noted that While a voltage doubler 47 is shown, any suitable source may be used other than the doubler 47.

What is claimed is:

1. A regulated power supply, adapted for connection to a voltage source, for providing pulses to a load, comprising:

a variable impedance device having a control electrode and two main electrodes, said voltage source being connectable to said load by way of said main electrodes;

means for supplying an operating bias to the electrodes of said device;

a voltage standard connectable across said voltage source;

first and second capacitors connected in series across said voltage standard; and

means by which said load can be connected across said second capacitor to cause said second capacitor to be charged initially to a voltage level related to the voltage across said voltage standard and subsequently to be charged through the path including the main electrodes of said variable impedance device.

2. The power supply according to claim 1 wherein said bias means comprises a second voltage source connected in series with the control electrode of said variable i1npedance device.

3. The power supply according to claim 1 further comprising:

a comparison device having a control electrode, a first main'electrode and a second main electrode, the first main electrode of said comparison device being connected to the control electrode of said regulating device, the second main electrode of said comparison device being connected in series with said voltage standard; and

means connected to the control electrode of said comparison device for providing a voltage which is a measure of the voltage across said load.

4. The power supply according to claim 1, wherein said voltage standard is a Zener diode.

5. The power supply according to claim 1, further comprising means for discharging said second capacitor through said load at predetermined times.

6. A regulated power supply, adapted for connection to a first and a second voltage source, for providing pulses to a load comprising:

a voltage regulating transistor having a base, a collector and an emitter electrode, said first voltage source being connectable in series with said load by way of the collector and emitter electrodes of said voltage regulating transistor;

a voltage comparison transistor having a base, a collector and an emitter electrode, the collector of the comparison transistor being connected at a junction point to the base of said regulating transistor, said second voltage source being connected to said junction point;

means connected between the emitter electrode of said regulating transistor and the base electrode of said means for discharging said second capacitor through comparison transistor for applying a voltage which is said load at predetermined times.

a measure of the voltage across said load to the base electrode of said comparison transistor; References Cited a voltage standard connectable across said first voltage UNITED STATES PATENTS source and in series with the collector and emitter 5 electrodes of said comparison transistor; g fif 5' 3- first and second capacitors connected in series across 3316445 4/1967 g 1 rons 3201 (X) voltage Standard 3 373 344 3/1968 Seer Jr 32322(T) means by which said load can be connected across said second capacitor to cause said second capacitor to be 10 charged initially to a voltage level related to the J D MILLER pnmafy Exammel:

voltage across said voltage standard and subsequently GOLDBERG, ASSlStant m er to be charged through the path including the emitter Us. CL

and olle tor lect 0d of 'd r ul ted tra itor;

and c c e r es Sal eg a 15 307-44, 294; 315-224, 232, 311; 320-4; 321-18 

